Although today’s nonprofit organizations make a strong appeal to vol- unteers, they often have difficulties with attracting and retaining these free labor forces. In this sense, studying the motivation of volunteers and its effects proves useful. In the present article, we investigate the relationship between volunteers’ motivation and their self-reported work effort, while relying on the Self-Determi- nation Theory. The results indicate a positive link between volunteers’ autonomous motivation and work effort. Moreover, this relationship holds for each person in our sample, irrespective of the organization in which she/he is volunteering. Implications for future research, as well as the practical impact of these findings, are discussed.